Hmm. No experience with those particular herbs (I normally use those that grow local to me- my familiars) but from everything I understand blue and black cohosh have a synergistic effect (they work better together.) I'm also fascinated to know what will slow down labour for some women but speed it up for others, other than a positive mindset.
Personally, I'm intending to stay away from anything that stimulates uterine contractions, eat lots and lots of blackberries (rubus negrus- same family as RRL and the active properties are present in fruits as well as leaves) and get lots of iron and vitamin K through nettle tea and soup- but then I'm weird like that. My standard tactic is firstly to do nothing, then to use vibrational remedies (like homoeopathy) and then herbal- but eating as nutritiously as possible.
Is there a reason you're expecting problems?